Magnetic recording medium

ABSTRACT

In a magnetic recording medium having an oxygen-containing thin ferromagnetic metal layer formed on a nonmagnetic substrate, at least one compound capable of suppressing the hydration of the ferromagnetic metal ions by acting thereon is located on or in the vicinity of the surface of the thin ferromagnetic metal layer. A lubricant may further be applied on the thin ferromagnetic metal layer.

BACKGROUND OF THE DISCLOSURE

1. Field of Invention

The present invention relates to a magnetic recording medium based on an electromagnetic conversion such as magnetic tapes, magnetic disks and so on.

2. Prior Art

A magnetic recording medium may be manufactured by depositing under vacuum conditions a thin ferromagnetic metal layer consisting mainly of Fe, Ni, Co or an alloy thereof on the surface of a base substrate composed of a non-magnetic material such as a plastic film, e.g. polyester, polyimide or the like, or an aluminum plate, a glass plate or the like, by means of deposition, ion plating, sputtering or other conventional techniques. The magnetic recording medium of this kind is suitable for high density recording such as recording of video signals. However, as the film thickness of the thin ferromagnetic metal layer is as small as 0.01 to 0.5 μm, corrosion is apt to occur on the surface of the magnetic recording medium in instances where it is exposed to highly moist atmospheres, particularly to atmospheres in which condensation is formed due to large variations in temperature. When corrosion has progressed to a certain extent, it has an effect on electromagnetic conversion performance and degrades working performance such as head touch, abrasion resistance and so on. Attempts have been made to control corrosion with an anti-corrosive agent; known anti-corrosive agents for a bulk metal such as Fe, Co, Ni or the like may be so employed.

Examples of such known anti-corrosive agents include a basic nitrogen compound such as an alkylamine or an aliphatic acid salt of an alkylamine; a phosphorus compound such as an alkyl phosphate, an alkyl thiophosphate, an alkyl hydrogen phosphoric acid ester or a phosphorus ester; a sulphonate such as petroleum sulphonate, mahogany acid sulphonate or dinonyl naphthalene sulphonate; a particular ester such as sorbitan monooleate or methyl ester of an organic acid; a particular carboxylic acid derivative such as a metallic soap of petroleum acid or of abietic acid or α-mercaptostearic acid; or a so-called volatile corrosion inhibitor such as dicyclohexylammonium nitrite, diisopropylammonium nitrite or cyclohexylamine carbamate. These bulk metal anti-corrosive agents are disclosed, for example, in "Manual of Metal Surface Technology", New Edition, Edited by Metal Surface Technology Association (1963; Publisher, Nikkan Kogyo Shimbunsha), pp. 1417 to 1439.

An oxygen-containing thin ferromagnetic metal layer formed by introducing a minute amount of oxygen gas into the vacuum system during the formation of the thin ferromagnetic metal layer is higher in coercive force than a layer containing no oxygen. Although the oxygen-containing thin ferromagnetic layer also provides an improved adhesive strength between the thin layer and the substrate and a greatly enhanced corrosion resistance, its corrosion resistance under severe atmospheres still is not satisfactory. Accordingly, such an anti-corrosive agent has been denounced as being inapplicable under severe conditions. It has now been found that anti-corrosive agents described hereinabove as being suitable for a thin ferromagnetic metal layer containing no oxygen, do not in fact impart a very good corrosion resistance to an oxygen-containing thin ferromagnetic metal layer, and in some cases they tend to accelerate corrosion.

The conventional bulk metal anti-corrosive agents are such that they act directly on the metal and stabilize the state of the metal surface. This phenomenon is described, for example, in "Rust preventing management" by Seiichi Fujii, 1978, Vol. 12, pp. 11 to 17. It is considered, however, that the surface of an oxygen-containing thin ferromagnetic metal layer is covered with an oxide layer of the ferromagnetic metal, and that when such a known anti-corrosive agent is used it penetrates through the oxide layer to act on the metal present therein, whereby the oxide layer cannot fulfil its purpose as a protective layer.

Therefore, it is now desired to use a new anti-corrosive agent for an oxygen-containing thin ferromagnetic metal layer, which is different from the conventional anti-corrosive agents.

A magnetic recording medium of the thin ferromagnetic metal layer type as described hereinabove provides an extremely high recording density compared with the conventional coated-type magnetic recording medium. This high-density recording also requires a spacing loss to be minimized and narrowing the gap of a magnetic head and at the same time flattening the surface of the magnetic recording medium. The spacing loss is required to be below 500 Å, and preferably below 300 Å. Although head touch and travel performance can be improved to a considerable extent by controlling the surface condition of the magnetic recording medium, it is essentially impossible to significantly decrease the contact area between the head and the medium, and to prevent an increase in a coefficient of friction.

The anti-corrosive agents to be used in the present invention contain a compound having a particular polar group bindable to a ferromagnetic metal ion. These anti-corrosive agents, by being adsorbed onto the thin ferromagnetic metal layer prevent rust from forming, but do not produce a very good effect in improving head touch and travel performance. It has been found that they rather have the drawback that they clog the gap of the head when applied in excess.

Although application of various lubricants has been proposed in order to reduce a coefficient of friction between the head and the magnetic recording medium, such lubricants excluding special ones do not exhibit the effect of rust resistance and in some cases they rather become a rust accelerating agent.

SUMMARY OF THE INVENTION Object of the Invention

It is an object of the present invention to provide a magnetic recording medium having an oxygen-containing thin ferromagnetic metal layer as a magnetic layer, having an enhanced corrosion resistance and at the same time having an improved travel performance and durability.

Constitution of the Invention

The present invention relates to a magnetic recording medium having an oxygen-containing thin ferromagnetic metal layer formed on a non-magnetic substrate, characterized in that a compound capable of suppressing hydration of the ferromagnetic metal ions by acting thereon is in the vicinity of said thin ferromagnetic metal layer, and also relates to a magnetic recording medium produced by further applying a lubricant to such a magnetic recording medium.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1, 2 and 3 are cross-sectional views illustrating the respective embodiments of the magnetic recording medium according to the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The non-magnetic substrate may comprise a film or sheet of a plastic such as a polyester, polyamide, polyimide or the like; a metallic plate consisting of aluminum, stainless steel or the like; or a ceramic plate or glass plate or the like. Since the surface configuration of the magnetic recording medium of the thin ferromagnetic metal layer type is largely dependent upon the surface configuration of the substrate, due to the thin metal layer formed thereon being usually as thin as 0.1 to 0.5 μm, it is particularly preferred to use a substrate produced so as to control its surface condition to a desired fineness, as disclosed in Japanese Patent Openings No. 116,115/1978, No. 16,937/1981 and No. 37,719/1982.

Such oxygen-containing thin ferromagnetic metal layers are disclosed in, for example, Japanese Patent Publication No. 23,208/1981 and Japanese Patent Openings No. 42,010/1978, No. 15,014/1981 and No. 37,719/1982.

The thin ferromagnetic layer which is obtained by carrying out continuous oblique deposition in a vacuum into which oxygen is introduced, is composed of an aggregate of fine, prismatic crystals. Each of the prismatic crystals is covered with an oxide layer of the ferromagnetic metal constituting the crystal. This oxide layer is at maximum as thin as 100 to 200 Å and there are many defects on its surface, such as crystal-structure defects or those derived from hydrates. In such defects, ferromagnetic metal ions, oxide ions and/or hydroxide ions are easily hydrated to become hydrated oxides of the ferromagnetic metal, that is, rust.

As a result of studies and review, it has been concluded that a compound capable of acting on the ionized ferromagnetic metal, that is, on its ions, its oxide ions and/or its hydroxide ions, and then of controlling the hydration of these ions, may be employed as a most appropriate anti-corrosive agent. Such a compound will be referred to merely as an "anti-corrosive agent" herein unless otherwise stated.

The anti-corrosive agents to be employed herein may be, for example, a dihydric phenol, a diaryl ketone, an alkylphenol, a naphthol, a quinone, a nitroso compound, an oxime compound and so on. These compounds will be described in more detail hereinbelow.

The dihydric phenols may include, for example, a true phenol such as hydroquinone, resorcin or catechol, or its alkylamino-, nitro-, nitroso- or halogen-substitution such as 2-methylhydroquinone, 4-methylresorcinol, 5-methylresorcinol, 4-methylpyrocatechol, 2,5-dimethylhydroquinone, 4,6-dimethylresorcinol, 2,5-dimethylresorcinol, 2-isopropyl-5-methylhydroquinone, 2-tert.-butylhydroquinone, 2,5-di-tert.-butylhydroquinone, 4-tert.-butylcatechol, 2-aminoresorcinol, 2-nitroresorcinol, 2,5-dichlorohydroquinone or the like.

The diaryl ketones may include, for example, benzophenone or a derivative thereof such as an alkyl substituted derivative including 4-methylbenzophenone, 3-methylbenzophenone, 3,4-dimethylbenzophenone, 4,4'-dimethylbenzophenone, 3,4'-dimethylbenzophenone, 4-ethylbenzophenone or the like; a hydroxybenzophenone including 4-hydroxybenzophenone, 4,4'-dihydroxybenzophenone, 2,3,4-trihydroxybenzophenone, 2,4-dihydroxybenzophenone, 2,2',5,6'-tetrahydroxybenzophenone, 2,3',4,4',6-pentahydroxybenzophenone or the like; an aminobenzophenone including 4-aminobenzophenone, 4,4'-diaminobenzophenone or the like; or a benzophenone having two or more substituents including 4-methoxy-2-hydroxybenzophenone, 2,2'-dihydroxy-4,4'dimethoxybenzophenone, 2,6-dihydroxy-4-methoxybenzophenone or the like.

The alkylphenols may include, for example, an alkyl substitution of a monohydric phenol, such as o-cresol, m-cresol, p-cresol, o-ethylphenol, m-ethylphenol, p-ethylphenol, 2,3-dimethylphenol, 2,5-dimethylphenol, 2,6-dimethylphenol, 3,4-dimethylphenol, 3,5-dimethylphenol, 2,4,6-trimethylphenol, 2,4,5-trimethylphenol, 5-isopropyl-2-methylphenol, 2-isopropyl-5-methylphenol, p-tert.-butyl-phenol, 2,6-di-tert.-butyl-p-cresol, 4,4'-methylenebis-2,6-di-tert.-butylphenol, 2,6-dimethyl-4-tert.-butylphenol, 2-tert.-amyl-4-methylphenol, 2-methyl-4,6-di-tert.-butylphenol, 2,4,6-tri-tert.-butylphenol or the like.

The naphthols may include, for example, a true naphthol such as α-naphthol, β-naphthol, 1,2-naphthalenediol, 1,4,5-naphthalenetriol, 1,2,5,8-naphthalenetetraol or the like, or a nitro-, nitroso-, amino- or halogen-substituted naphthol such as 1-chloro-2-naphthol, 2,4-dichloro-1-naphthol, 1-nitro-2-naphthol, 1,6-dinitro-2-naphthol, 1-nitroso-2-naphthol, 2-nitroso-1-naphthol, 1-amino-2-naphthol or the like.

The quinones may include, for example, an unsubstituted quinone such as p-benzoquinone, o-benzoquinone, 1,2-naphthoquinone, 1,4-naphthoquinone, 2,6-naphthoquinone, anthraquinone, 9,10-phenanthrenequinone, diphenoquinone or the like; a methylquinone such as methyl-p-benzoquinone, 2,3-dimethyl-p-benzoquinone, 2-methyl-1,4-naphthoquinone, 2-methylanthraquinone or the like, a hydroxyquinone such as 2,5-dihydroxy-p-benzoquinone, tetrahydroxy-p-benzoquinone, 5-hydroxy-1,4-naphthoquinone, 2,3-dihydroxy-1,4-naphthoquinone, 5,8-dihydroxy-1,4-naphthoquinone, 2-hydroxyanthraquinone, 1,2-dihydroxyanthraquinone, 1,2,3-trihydroxyanthraquinone, 1,2,4-trihydroxyanthraquinone, 1,2,5-trihydroxyanthraquinone, 1,2,6-trihydroxyanthraquinone, 1,2,7-trihydroxyanthraquinone or the like; an aminoquinone such as 2-aminoanthraquinone, 1,2-diaminoanthraquinone or the like; a nitroquinone such as 1-nitroanthraquinone, 1,5-dinitroanthraquinone or the like; a halogenoquinone such as 2,6-dichloro-p-benzoquinone, tetrachloro-p-benzoquinone, tetrafluoro-p-benzoquinone or the like; or a quinone having two or more substituents such as 2,5-dichloro-3,6-dihydroxy-p-benzoquinone, 1-methyl-2-hydroxy-1,4-naphthoquinone or the like.

The nitroso compound may be an organic compound having both a hydroxy group and a nitroso group, such as one of the nitrosophenol series and the nitrosonaphthol series. Specifically, it may be selected from 1-nitroso-2-naphthol, 2-nitroso-1-naphthol, 1-nitroso-2-naphthol-3,6-disulphonic acid sodium salt (nitroso R salt), 4-nitroso-2-methoxy-1-phenol, 4-nitroso-2-ethoxy-1-phenol, 4-nitrosocarvacrol, 6-nitroso-o-cresol, 4-nitroso-m-cresol, o-nitrosophenol, 2-nitrosoresorcin, 4-nitrosoresorcin, 2-nitrosoresorcin monomethylether, N-nitrosophenyl hydroxylamine ammonium salt (cupferron), p-nitrosophenol, 2-nitroso-1-naphthol-4-sulphonic acid, 5-nitroso-8-quinolinol or the like.

The oxime compounds may include, for example, benzyloxime, glyoxime, benzaldoxime, benzamidoxime, α-benzoinoxime, acetophenone oxime, benzophenone oxime, dimethylglyoxime, salicylaldoxime or the like.

These anti-corrosive agents produce their effects when they are present at least on the surface of the thin ferromagnetic layer and preferably within the layer or at the interface thereof with the substrate on which the thin ferromagnetic layer is formed. The amount of the anti-corrosive agent ranges preferably from about 0.5 to 500 mg per square meter of the magnetic recording medium. The anti-corrosive agent may be applied to the thin ferromagnetic metal layer by, for example, the coating technique by which the anti-corrosive agent to be used is admixed with a substance such as a polymer substance having a film forming ability, and the resulting mixture is coated thereon after dilution, if necessary, with a suitable solvent; by a technique in which a vapor of the anti-corrosive agent is applied thereto; by a transfer technique in which the anti-corrosive agent is applied to the rear surface of the magnetic recording medium and is transferred to the front surface thereof when the tape is wound in a roll; and by any other conventional technique.

It is also possible to apply a thin ferromagnetic metal layer to a nonmagnetic substrate containing an anticorrosive agent, where the anti-corrosive agent is introduced into the side surface of the substrate with which it has been brought into contact.

The substrate containing the anti-corrosive agent may be prepared by forming numerous minute pores at least on the surface of the substrate by means of etching or the like, and by permitting the anti-corrosive agent to enter the pores. Plastic substrates may be prepared, for example, by adding the anti-corrosive agent to a substrate raw material or to an agent for providing a surface shape when coatings are applied, or by diffusing the anti-corrosive agent through the substrate by means of immersion thereof in an anti-corrosive agent solution. The anti-corrosive agent may be present homogeneously within a nonmagnetic substrate, or in the vicinity of a surface thereof in a localized manner. It may also be segregated in a finely divided form. It is desirable that the anti-corrosive agent be present on at least one of the substrate surfaces on which the magnetic layer is formed.

The amount of anti-corrosive agent in or on the nonmagnetic substrate may be in the range of 0.001 to 10% by weight, and preferably 0.01 to 1% by weight at least in the vicinity of the surface on which the magnetic layer is formed, to within a depth of about 1,000 Å from the surface. The amount of anti-corrosive agent present deeper within the substrate may be equal to or smaller than that in the vicinity of the surface.

It is further noted that the anti-corrosive agents as described hereinabove may be employed singly or in combination with each other. In order to further enhance the effect of the anti-corrosive agent on the thin ferromagnetic metal layer, it is possible to subject the thin ferromagnetic metal layer to heat treatment after the application of the anti-corrosive agent. If an excess of the anti-corrosive agent is adhered to the surface of the thin ferromagnetic metal layer, an excess of the anti-corrosive agent may be removed by washing the surface of the thin layer with a solvent capable of selectively dissolving the anti-corrosive agent. The anti-corrosive agent may usually be adsorbed at particular sites of the surface of the thin ferromagnetic metal layer by means of chemical adsorption or in such a manner similar thereto that it may not be removed merely by washing with a solvent. This may be assumed from the fact that a sufficient degree of anti-corrosion is achieved even after washing with the solvent; it may also be determined by measurement of the chemical shift by means of X-ray photoelectric spectrometry (ESCA).

As described under the conventional examples, the anti-corrosive agent to be used in accordance with the present invention does not provide sufficient improvement in a coefficient of friction between the magnetic recording medium and a magnetic head or a rotary cylinder or the like, so that the additional use of a lubricant is necessary if high lubrication of the magnetic recording medium is required. Procedures for providing further lubrication of the magnetic recording medium are as follows:

(1) Forming a lubricant layer on the external surface of a thin ferromagnetic metal layer at or in the vicinity of the interface thereof with the anti-corrosive agent; and

(2) Forming a thin ferromagnetic metal layer on one of the surfaces of a flexible, elongated, nonmagnetic substrate in such a manner that the anti-corrosive agent may be introduced on or in the vicinity of the surface of the thin ferromagnetic metal layer, and forming a lubricant layer or a lubricant-containing resinous layer on the other substrate surface.

FIGS. 1 through 3 illustrate respective embodiments of the magnetic recording medium formed according to procedure 1 above. In the drawings, reference numerals 1, 1' and 1" denote substrates; 2, 2' and 2", thin ferromagnetic metal layers; 3, 3' and 3", adsorbed layers of the anti-corrosive agent; and 4, 4', and 4", lubricant layers respectively. Reference numeral 5" is an oxide layer of the ferromagnetic metal covering the surface of the oxygen-containing thin ferromagnetic metal layer. In the embodiment as shown in FIG. 1, the lubricant layer 4 is adsorbed homogeneously onto the anti-corrosive layer 3. In the embodiment as shown in FIG. 2, the lubricant layer 4' is aggregated and adsorbed onto the anti-corrosive agent 3' in an island form. FIG. 3 is a view illustrating more microscopically than in FIGS. 1 and 2, which is provided by obliquely depositing a ferromagnetic metal in the presence of a minute amount of oxygen. In this embodiment, the layer 3" of the anti-corrosive agent is adsorbed onto the thin ferromagnetic metal layer 2" which is composed of a prismatic crystal structure covered at its surface with the oxide layer and further provided at its surface with the lubricant layer 4". As is apparent from these embodiments, the magnetic recording medium according to the present invention is constructed such that the thin ferromagnetic metal layer is covered with the anti-corrosive agent layer so that a favorable corrosion resistance is achieved, and a coefficient of friction with a magnetic head is reduced, due to the aid of the lubricant layer present on the surface of the magnetic recording medium, enhancing an abrasion resistance of the surface of the magnetic recording medium upon repeated travel. It is surprisingly found that the adsorption of the lubricant onto the thin ferromagnetic metal layer through the anti-corrosive agent layer is more stable than in the case where the lubricant is adsorbed directly onto the thin ferromagnetic metal layer.

The lubricant layer may be composed in a manner as described hereinbelow. It may contain an antistatic agent and/or a fungicide as required.

As the lubricant there may be employed an aliphatic acid, an aliphatic acid ester, an aliphatic acid amide, a metallic soap, an aliphatic alcohol, a paraffin, a silicone and a fluorine-type surface active agent. Among these lubricants, some aliphatic acids, fluorine-type surface active agents and so on can impart a corrosion resistance to a thin ferromagnetic metal layer and their effect is further enchanced by the aid of the anti-corrosive agent layer interposed therebetween as compared to the use of such a lubricant alone. It is accordingly particularly appropriate to employ such a lubricant for the present invention.

The aliphatic acid may be, for example, an acid having from 12 to 22 carbon atoms such as lauric acid, myristic acid, palmitic acid, stearic acid, behenic acid, oleic acid, linoleic acid, linolenic acid or the like.

The aliphatic acid ester may be, for example, ethyl stearate, butyl stearate, amyl stearate, stearic acid monoglyceride, palmitic acid monoglyceride, oleic acid monoglyceride, pentaerythritol tetrastearate or the like.

The aliphatic acid amide may be, for example, caproic acid amide, caprylic acid amide, lauric acid amide, palmitic acid amide, stearic acid amide, behenic acid amide, oleic acid amide, linoleic acid amide, methylenebisstearic acid amide, ethylenebisstearic acid amide or the like.

The metallic soap may comprise a salt of an acid such as lauric acid, myristic acid, palmitic acid, stearic acid, behenic acid, oleic acid, linoleic acid, linolenic acid or the like with a metal such as zinc, lead, nickel, cobalt, iron, aluminum, magnesium, strontium, copper or the like; or a salt of a sulphonate of an acid such as lauric acid, palmitic acid, myristic acid, stearic acid, behenic acid, oleic acid, linoleic acid, linolenic acid or the like with one of the above-described metals.

The aliphatic alcohol may be, for example, cetyl alcohol, stearyl alcohol or the like.

The paraffin may be, for example, a saturated hydrocarbon such as n-octadecane, n-nonadecane, n-tridecane, n-docosane, n-dotriacontane or the like.

The silicone may be, for example, a polysiloxane having its hydrogen or hydrogens partially substituted by an alkyl group or a phenyl group, and those modified with an aliphatic acid, an aliphatic alcohol, an acid amide or the like.

The fluorine-type surface active agent may comprise a salt of an acid such as perfluoroalkylcarboxylic acid or perfluoroalkylsulfonic acid with a metal such as sodium, potassium, magnesium, zinc, aluminum, iron, cobalt, nickel or the like; perfluoroalkyl phosphoric ester; perfluoroalkyl betaine; perfluoroalkyltrimethyl ammonium salt; perfluoroethylene oxide; perfluoroalkyl aliphatic ester; or the like.

These lubricants may be employed singly or in combination with each other. The lubricant layer may be heat-treated after the formation thereof in order to stabilize the lubricant layer.

The thickness of the lubricant layer should generally be less than 500 Å, and preferably less than 200 Å. In instances where the thin ferromagnetic metal layer is a prismatic crystal structure formed by means of oblique deposition or the like, the lubricant layer may be formed over a whole area of the prismatic crystals as shown in FIG. 3. It is also possible to produce the effect which is the object of the present invention by exposing the lubricant on the surface in a localized manner.

In the above-described embodiments, it is possible to add the anti-corrosive agent to the lubricant layer or to mix the former with the lubricant. Improved anti-corrosion may be obtained by introducing a slightly excessive amount of the anti-corrosive agent onto the surface of the thin ferromagnetic metal layer.

The magnetic recording medium as embodied in item 2 above will now be described in more detail.

The formation of the lubricant layer may comprise allowing the lubricant or a mixture thereof to adhere directly to the surface of a nonmagnetic substrate or to a back coating formed on the nonmagnetic substrate. Specifically, a dilution of the lubricant with a solvent may be applied in a thin coating or a vapor of the lubricant may be applied to the surface of the non-magnetic substrate or to the back coating. In this case, it is possible to add to the lubricant an antistatic agent, a fungicide or the anti-corrosive agent to be adsorbed into the magnetic surface. The amount of the lubricant to be adhered may be generally in the range of 0.5 to 500 mg/m², and preferably 5 to 200 mg/m² of the magnetic recording medium.

Other procedures for forming the lubricant layer are to incorporate the lubricant in the back coating and then to convert the lubricant into the lubricant layer useful for the magnetic recording medium according to the present invention. Specifically, the back coating may be formed by coating a solution or a dispersion of fine powders in a solution of a resin on the surface of a nonmagnetic substrate, said resin being selected from the group including those of vinyl chloride types, ester types, urethane types, epoxy types or the like. The lubricant to be used in accordance with the present invention may include, for example, fine powders of carbon black, graphite, molybdenum disulfide, calcium carbonate, silica, alumina or the like.

The thickness of the back coating may be in the range of 0.01 to 0.5 μm. The amount of the lubricant contained in the coating may be appropriately within the range of 0.1 to 50% of the volume of the coating. Added to this back coating may be an antistatic agent, a fungicide or the anti-corrosive agent to be adsorbed onto the surface of the magnetic layer.

In instances where the anti-corrosive agent is added to the lubricant layer, the anti-corrosive agent is transferred to the magnetic surface together with the lubricant when the magnetic recording medium is wound in a roll, thereby preventing the abrasion of the surface of the magnetic layer in practical running and the deterioration of the corrosion resistance on portions of the magnetic layers on which damage such as cracking occurs. For similar reasons, a slightly excessive amount of the anti-corrosive agent may be present on the anti-corrosive agent layer provided on the magnetic layer surface. When the amount of the anti-corrosive agent present on the anti-corrosive agent layer is too much, it may cause clogging of a magnetic head. The amount of such anti-corrosive agent may be at maximum 100 mg, and preferably from 5 to 50 mg/m² of the magnetic recording medium. Within this limit, the transfer of the lubricant to the magnetic surface may be performed without clogging. This is one of the effects achieved by the present invention.

In order to complete the transfer of the lubricant to the magnetic surface, it is possible, if necessary, to subject the magnetic recording medium in a roll form to heat treatment immediately after manufacture. The heat-treatment may be performed at 30° to 60° C. for 1 to 50 hours.

EXAMPLE 1

A polyester film having a thickness of 10 μm was run along a cylindrical can in a vacuum of 5×10⁻⁵ Torr into which oxygen was introduced at the rate of 0.3 l/min. In this vacuum device, a CoNi alloy (having an Ni content of 20% by weight) which was fused by electron beam heating was obliquely deposited on the polyester film. The alloy of an incident angle of 30° or less was cut off. Thus, there was formed an oxygen-containing CoNi thin ferromagnetic metal layer having a thickness of 1,000 Å. This will be referred to as Sample A.

Another sample was prepared in substantially the same manner with the exception that the CoNi thin ferromagnetic metal layer was formed in a vacuum of 5×10⁻⁶ Torr into which no oxygen was introduced. This will be referred to as Sample B.

From measurement of the amount of oxygen in the coating by means of the Auger electron spectrometry analysis, it was found that the average amount of oxygen in the coating of Sample A was 10% as an atomic ratio of oxygen to the sum of Co and Ni atoms (Oxygen/(Co+Ni)×100), whereas the average amount of oxygen in the coating of Sample B was less than 1%.

For observing the occurrence of rust, samples were prepared by coating a solution of various anti-corrosive agents in water, ethylalcohol, acetone, toluene or the like so as to form a coating of 10 mg/m² to 100 mg/m². The occurrence of rust was measured periodically in an atmosphere in which the temperature was maintained at 50° C. and the moisture at 90% relative humidity. The results are shown in Tables 1 through 6 which follow.

As will be apparent from the results shown in the following tables, the anti-corrosive agents to be used in accordance with the present invention have significant anti-corrosive effects on oxygen-containing CoNi thin layers. Particularly favorable effects were obtained on the CoNi thin layers having an oxygen content in the range of 3 to 45% and an Ni content in the range of 10 to 55% by weight. Analogous results were obtained on Co thin layers, Fe-Ni thin layers, Fe-Co thin layers and so on.

                                      TABLE 1                                      __________________________________________________________________________     Examples                  Rust occurrence                                      No.      Anti-corrosive agents                                                                          Sample A                                                                               Sample B                                      __________________________________________________________________________     1        hydroquinone    No rust in 5                                                                           Rust occurred                                                          weeks   within 1 week                                 2        resorcin        No rust in 5                                                                           Rust occurred                                                          weeks   within 1 week                                 3        catechol        No rust in 5                                                                           Rust occurred                                                          weeks   within 1 week                                 4        2-methylhydroquinone                                                                           No rust in 5                                                                           Rust occurred                                                          weeks   within 1 week                                 5        4-methylresorcinol                                                                             No rust in 5                                                                           Rust occurred                                                          weeks   within 1 week                                 6        5-methylresorcinol                                                                             No rust in 5                                                                           Rust occurred                                                          weeks   within 1 week                                 7        4-methylpyrocatechol                                                                           No rust in 5                                                                           Rust occurred                                                          weeks   within 1 week                                 8        2,5-dimethylhydroquinone                                                                       No rust in 5                                                                           Rust occurred                                                          weeks   within 1 week                                 9        4,6-dimethylresorcinol                                                                         No rust in 5                                                                           Rust occurred                                                          weeks   within 1 week                                 10       2,5-dimethylresorcinol                                                                         No rust in 5                                                                           Rust occurred                                                          weeks   within 1 week                                 11       2-isopropyl-5-methyl-                                                                          Rust occurred                                                                          Rust occurred                                          hydroquinone    after 5 weeks                                                                          within 1 week                                 12       2-tert.-butylhydro-                                                                            Rust occurred                                                                          Rust occurred                                          quinone         after 5 weeks                                                                          within 1 week                                 13       2,5-di-tert.-butylhydro-                                                                       Rust occurred                                                                          Rust occurred                                          quinone         after 5 weeks                                                                          within 1 week                                 14       4-tert.-butylcatechol                                                                          No rust in 5                                                                           Rust occurred                                                          weeks   within 1 week                                 15       2-aminoresorcinol                                                                              No rust in 5                                                                           Rust occurred                                                          weeks   within 1 week                                 16       2-nitroresorcinol                                                                              Rust occurred                                                                          Rust occurred                                                          after 5 weeks                                                                          within 1 week                                 17       2,5-dichlorohydro-                                                                             Rust occurred                                                                          Rust occurred                                          quinone         after 5 weeks                                                                          within 1 week                                 18       hydroquinone 50%                                                                               No rust in 5                                                                           Rust occurred                                          2-tert.-butylhydro-                                                                            weeks                                                          quinone      50%        within 1 week                                 19       catechol     50%                                                                               No rust in 5                                                                           Rust occurred                                          β-naphthol                                                                             50%                                                                               weeks   within 1 week                                 20       hydroquinone 50%                                                                               No rust in 5                                                                           Rust occurred                                          p-benzoquinone                                                                              50%                                                                               weeks   within 1 week                                 21       resorcin     50%                                                                               No rust in 5                                                                           Rust occurred                                          anthracene   50%                                                                               weeks   within 1 week                                 Comparative                                                                             (Excluding any anti-                                                                           Rust occurred                                                                          Rust occurred                                 Example  corrosive agent)                                                                               after 2 weeks                                                                          within 1 week                                 __________________________________________________________________________

                                      TABLE 2                                      __________________________________________________________________________     Examples                Rust occurrence                                        No.    Anti-corrosive agents                                                                          Sample A                                                                               Sample B                                        __________________________________________________________________________     1      benzophenone    No rust in 5                                                                           Rust occurred                                                          weeks   within 1 week                                   2      4-methylbenzophenone                                                                           No rust in 5                                                                           Rust occurred                                                          weeks   within 1 week                                   3      3-methylbenzophenone                                                                           No rust in 5                                                                           Rust occurred                                                          weeks   within 1 week                                   4      3,4-dimethylbenzo-                                                                             Rust occurred                                                                          Rust occurred                                          phenone         in 5 weeks                                                                             within 1 week                                   5      4,4' -dimethylbenzo-                                                                           Rust occurred                                                                          Rust occurred                                          phenone         after 5 weeks                                                                          within 1 week                                   6      3,4' -dimethylbenzo-                                                                           Rust occurred                                                                          Rust occurred                                          phenone         after 5 weeks                                                                          within 1 week                                   7      4-ethylbenzophenone                                                                            No rust in 5                                                                           Rust occurred                                                          weeks   within 1 week                                   8      4-hydroxybenzophenone                                                                          No rust in 5                                                                           Rust occurred                                                          weeks   within 1 week                                   9      4,4'-dihydroxybenzo-                                                                           No rust in 5                                                                           Rust occurred                                          phenone         weeks   within 1 week                                   10     2,3,4-trihydroxybenzo-                                                                         No rust in 5                                                                           Rust occurred                                          phenone         weeks   within 1 week                                   11     2,4-dihydroxybenzo-                                                                            No rust in 5                                                                           Rust occurred                                          phenone         weeks   within 1 week                                   12     2,2' ,5,6'-tetrahydro                                                                          Rust occurred                                                                          Rust occurred                                          benzophenone    after 5 weeks                                                                          within 1 week                                   13     2,3' ,4,4' ,6-pentahydroxy                                                                     Rust occurred                                                                          Rust occurred                                          benzophenone    after 5 weeks                                                                          within 1 week                                   14     4-aminobenzophenone                                                                            No rust in 5                                                                           Rust occurred                                                          weeks   within 1 week                                   15     4,4'-diaminobenzophenone                                                                       No rust in 5                                                                           Rust occurred                                                          weeks   within 1 week                                   16     4-methoxy-2-hydroxy-                                                                           No rust in 5                                                                           Rust occurred                                          benzophenone    weeks   within 1 week                                   17     2,2'-dihydroxy-4,4'-                                                                           No rust in 5                                                                           Rust occurred                                          dimethoxybenzophenone                                                                          weeks   within 1 week                                   18     2,6-dihydroxy-4-                                                                               No rust in 5                                                                           Rust occurred                                          methoxybenzophenone                                                                            weeks   within 1 week                                   19     benzophenone 50%                                                                               No rust in 5                                                                           Rust occurred                                          hydroquinone 50%                                                                               weeks   within 1 week                                   20     benzophenone 50%                                                                               No rust in 5                                                                           Rust occurred                                          anthracene   50%                                                                               weeks   within 1 week                                   Comparative                                                                           (Excluding any anti-                                                                           Rust occurred                                                                          Rust occurred                                   Examples                                                                              corrosive agent)                                                                               after 2 weeks                                                                          within 1 week                                   __________________________________________________________________________

                  TABLE 3                                                          ______________________________________                                         Exam-                                                                          ples             Rust occurrence                                               No.   Anti-corrosive agents                                                                         Sample A    Sample B                                      ______________________________________                                         1     o-cresol       Rust occurred                                                                              Rust occurred                                                      after 5 weeks                                                                              within 1 week                                 2     m-cresol       Rust occurred                                                                              Rust occurred                                                      after 5 weeks                                                                              within 1 week                                 3     p-cresol       Rust occurred                                                                              Rust occurred                                                      after 5 weeks                                                                              within 1 week                                 4     o-ethylphenol  Rust occurred                                                                              Rust occurred                                                      after 5 weeks                                                                              within 1 week                                 5     m-ethylphenol  No rust in 5                                                                               Rust occurred                                                      weeks       within 1 week                                 6     p-ethylphenol  No rust in 5                                                                               Rust occurred                                                      weeks       within 1 week                                 7     2,3-dimethylphenol                                                                            Rust occurred                                                                              Rust occurred                                                      after 5 weeks                                                                              within 1 week                                 8     2,4-dimethylphenol                                                                            No rust in 5                                                                               Rust occurred                                                      weeks       within 1 week                                 9     2,5-dimethylphenol                                                                            No rust in 5                                                                               Rust occurred                                                      weeks       within 1 week                                 10    2,6-dimethylphenol                                                                            No rust in 5                                                                               Rust occurred                                                      weeks       within 1 week                                 11    3,4-dimethylphenol                                                                            No rust in 5                                                                               Rust occurred                                                      weeks       within 1 week                                 12    3,5-dimethylphenol                                                                            No rust in 5                                                                               Rust occurred                                                      weeks       within 1 week                                 13    2,4,6-trimethylphenol                                                                         No rust in 5                                                                               Rust occurred                                                      weeks       within 1 week                                 14    2,4,5-trimethylphenol                                                                         Rust occurred                                                                              Rust occurred                                                      after 5 weeks                                                                              within 1 week                                 15    5-isopropyl-2- No rust in 5                                                                               Rust occurred                                       methylphenol   weeks       within 1 week                                 16    2-isopropyl-5- No rust in 5                                                                               Rust occurred                                       methylphenol   weeks       within 1 week                                 17    p-tert.-butylphenol                                                                           No rust in 5                                                                               Rust occurred                                                      weeks       within 1 week                                 18    2,6-di-tert.-butyl-p-                                                                         No rust in 5                                                                               Rust occurred                                       cresol         weeks       within 1 week                                 19    4,4'-methylenebis-2,6-                                                                        No rust in 5                                                                               Rust occurred                                       di-tert.-butylphenol                                                                          weeks       within 1 week                                 20    2,6-dimethyl-4-tert.-                                                                         No rust in 5                                                                               Rust occurred                                       butylphenol    weeks       within 1 week                                 21    2-tert.-amyl-4-methyl-                                                                        No rust in 5                                                                               Rust occurred                                       phenol         weeks       within 1 week                                 22    2-methyl-4,6-di-tert.-                                                                        No rust in 5                                                                               Rust occurred                                       butylphenol    weeks       within 1 week                                 23    2-methyl-4,6-di-tert.-                                                                        No rust in 5                                                                               Rust occurred                                       butylphenol    weeks       within 1 week                                 24    2,4,6-tri-tert.-butyl-                                                                        No rust in 5                                                                               Rust occurred                                       phenol         weeks       within 1 week                                 25    2,3-dimethylphenol,                                                                           No rust in 5                                                                               Rust occurred                                       hydroquinone   weeks       within 1 week                                 26    p-tert-butylphenol                                                                            No rust in 5                                                                               Rust occurred                                       β-naphthol                                                                               weeks       within 1 week                                 Com-   (Excluding any anti-                                                                         Rust occurred                                                                              Rust occurred                                 para- corrosive agent)                                                                              after 2 weeks                                                                              within 1 week                                 tive                                                                           Exam-                                                                          ple                                                                            ______________________________________                                    

                                      TABLE 4                                      __________________________________________________________________________     Exam-                                                                          ples                   Rust occurrence                                         No.      Anti-corrosive agents                                                                        Sample A                                                                               Sample B                                        __________________________________________________________________________     1        α-naphthol                                                                             No rust in 5                                                                           Rust occurred                                                          weeks   within 1 week                                   2        β-naphthol                                                                              No rust in 5                                                                           Rust occurred                                                          weeks   within 1 week                                   3        1,2-naphthalenediol                                                                          No rust in 5                                                                           Rust occurred                                                          weeks   within 1 week                                   4        1,4,5-naphthalenetriol                                                                       No rust in 5                                                                           Rust occurred                                                          weeks   within 1 week                                   5        1,2,5,8-naphthalene-                                                                         No rust in 5                                                                           Rust occurred                                            tetraol       weeks   within 1 week                                   6        1-chloro-2-naphthol                                                                          No rust in 5                                                                           Rust occurred                                                          weeks   within 1 week                                   7        2,4-dichloro-1-naphthol                                                                      No rust in 5                                                                           Rust occurred                                                          weeks   within 1 week                                   8        1-nitro-2-naphthol                                                                           Rust occurred                                                                          Rust occurred                                                          after 5 weeks                                                                          within 1 week                                   9        1,6-dinitro-2-naphthol                                                                       Rust occurred                                                                          Rust occurred                                                          after 5 weeks                                                                          within 1 week                                   10       1-nitroso-2-naphthol                                                                         No rust in 5                                                                           Rust occurred                                                          weeks   within 1 week                                   11       2-nitroso-1-naphthol                                                                         No rust in 5                                                                           Rust occurred                                                          weeks   within 1 week                                   12       1-amino-2-napthol                                                                            No rust in 5                                                                           Rust occurred                                                          weeks   within 1 week                                   13       α-naphthol                                                                          50%                                                                               No rust in 5                                                                           Rust occurred                                            1-nitro-2-naphthol                                                                        50%                                                                               weeks   within 1 week                                   14       1-amino-2-naphthol                                                                        50%                                                                               No rust in 5                                                                           Rust occurred                                            p-aminophenol                                                                             50%                                                                               weeks   within 1 week                                   15       α-naphthol                                                                          50%                                                                               No rust in 5                                                                           Rust occurred                                            anthracene 50%                                                                               weeks   within 1 week                                   Comparative                                                                             (Excluding any anti-                                                                         Rust occurred                                                                          Rust occurred                                   Exam-    corrosive agent)                                                                             after 2 weeks                                                                          within 1 week                                   ples                                                                           __________________________________________________________________________

                                      TABLE 5                                      __________________________________________________________________________     Exam-                                                                          ples                     Rust occurrence                                       No.      Anti-corrosive agents                                                                          Sample A                                                                               Sample B                                      __________________________________________________________________________     1        p-benzoquinone  No rust in 5                                                                           Rust occurred                                                          weeks   within 1 week                                 2        o-benzoquinone  No rust in 5                                                                           Rust occurred                                                          weeks   within 1 week                                 3        1,2-naphthoquinone                                                                             No rust in 5                                                                           Rust occurred                                                          weeks   within 1 week                                 4        1,4-naphthoquinone                                                                             No rust in 5                                                                           Rust occurred                                                          weeks   within 1 week                                 5        2,6-naphthoquinone                                                                             No rust in 5                                                                           Rust occurred                                                          weeks   within 1 week                                 6        anthraquinone   No rust in 5                                                                           Rust occurred                                                          weeks   within 1 week                                 7        9-10-phenanthrene-                                                                             No rust in 5                                                                           Rust occurred                                          quinone         weeks   within 1 week                                 8        diphenoquinone  No rust in 5                                                                           Rust occurred                                                          weeks   within 1 week                                 9        methyl-p-benzoquinone                                                                          Rust occurred                                                                          Rust occurred                                                          after 5 weeks                                                                          within 1 week                                 10       2,3-dimethyl-p-benzo-                                                                          Rust occurred                                                                          Rust occurred                                          quinone         after 5 weeks                                                                          within 1 week                                 11       2-methy-1,4-naphtho-                                                                           No rust in 5                                                                           Rust occurred                                          quinone         weeks   within 1 week                                 12       2-methylanthraquinone                                                                          No rust in 5                                                                           Rust occurred                                                          weeks   within 1 week                                 13       2,5-dihydroxy-p-benzo-                                                                         No rust in 5                                                                           Rust occurred                                          quinone         weeks   within 1 week                                 14       tetrahydroxy-p-benzo-                                                                          No rust in 5                                                                           Rust occurred                                          quinone         weeks   within 1 week                                 15       5-hydroxy-1,4-naphtho-                                                                         No rust in 5                                                                           Rust occurred                                          quinone         weeks   within 1 week                                 16       2,3-dihydroxy-1,4-                                                                             No rust in 5                                                                           Rust occurred                                          naphthoquinone  weeks   within 1 week                                 17       5,8-dihydroxy-1,4-                                                                             No rust in 5                                                                           Rust occurred                                          naphthoquinone  weeks   within 1 week                                 18       2-hydroxyanthraquinone                                                                         No rust in 5                                                                           Rust occurred                                                          weeks   within 1 week                                 19       1,2-dihydroxyanthra-                                                                           No rust in 5                                                                           Rust occurred                                          quinone         weeks   within 1 week                                 20       1,2,3-trihydroxyanthra-                                                                        No rust in 5                                                                           Rust occurred                                          quinone         weeks   within 1 week                                 21       1,2,4-trihydroxyanthra-                                                                        No rust in 5                                                                           Rust occurred                                          quinone         weeks   within 1 week                                 22       1,2,5-trihydroxyanthra-                                                                        No rust in 5                                                                           Rust occurred                                          quinone         weeks   within 1 week                                 23       1,2,6-trihydroxyanthra-                                                                        No rust in 5                                                                           Rust occurred                                          quinone         weeks   within 1 week                                 24       1,2,7-trihydroxyanthra-                                                                        No rust in 5                                                                           Rust occurred                                          quinone         weeks   within 1 week                                 25       2-amino-anthraquinone                                                                          Rust occurred                                                                          Rust occurred                                                          after 5 weeks                                                                          within 1 week                                 26       1,2-diaminoanthra-                                                                             No rust in 5                                                                           Rust occurred                                          quinone         weeks   within 1 week                                 27       1-nitroanthraquinone                                                                           Rust occurred                                                                          Rust occurred                                                          after 4 weeks                                                                          within 1 week                                 28       1,5-dinitroanthra-                                                                             Rust occurred                                                                          Rust occurred                                          quinone         after 3 weeks                                                                          within 1 week                                 29       2,6-dichloro-p-benzo-                                                                          Rust occurred                                                                          Rust occurred                                          quinone         after 4 weeks                                                                          within 1 week                                 30       tetrachloro-p-benzo-                                                                           Rust occurred                                                                          Rust occurred                                          quinone         after 4 weeks                                                                          within 1 week                                 31       tetrabromo-p-benzo-                                                                            Rust occurred                                                                          Rust occurred                                          quinone         after 3 weeks                                                                          within 1 week                                 32       2,5-dichloro-3,6-di-                                                                           Rust occurred                                                                          Rust occurred                                          hydroxy-p-benzoquinone                                                                         after 5 weeks                                                                          within 1 week                                 33       1-methyl-2-hydroxy-p-                                                                          No rust in 5                                                                           Rust occurred                                          benzoquinone    weeks   within 1 week                                 34       1-methyl-2-hydroxy-1,4-                                                                        No rust in 5                                                                           Rust occurred                                          naphthoquinone  weeks   within 1 week                                 35       1,2-naphthoquinone                                                                         (50%)                                                                              No rust in 5                                                                           Rust occurred                                          2,3-dihydroxy-1,4-                                                                             weeks   within 1 week                                          naphthoquinone                                                                             (50%)                                                     36       anthraquinone                                                                              (50%)                                                                              No rust in 5                                                                           Rust occurred                                          anthracene  (50%)                                                                              weeks   within 1 week                                 Comparative                                                                             (Excluding any anti-                                                                           Rust occurred                                                                          Rust occurred                                 Exam-    corrosive agent)                                                                               after 2 weeks                                                                          within 1 week                                 ple                                                                            __________________________________________________________________________

                                      TABLE 6                                      __________________________________________________________________________     Exam-                                                                          ples                 Rust occurrence                                           No.    Anti-corrosive agents                                                                        Sample A                                                                               Sample B                                          __________________________________________________________________________     1      1-nitroso-2-naphthol                                                                         No rust in 5                                                                           Rust occurred                                                          weeks   within 1 week                                     2      2-nitroso-1-naphthol                                                                         No rust in 5                                                                           Rust occurred                                                          weeks   within 1 week                                     3      disodium 1-nitroso-2-                                                                        Rust occurred                                                                          Rust occurred                                            naphthol-3,6-disulfonate                                                                     after 5 weeks                                                                          within 1 week                                     4      4-nitroso-2-methoxy-                                                                         Rust occurred                                                                          Rust occurred                                            l-phenol      after 5 weeks                                                                          within 1 week                                     5      4-nitroso-2-ethoxy-                                                                          Rust occurred                                                                          Rust occurred                                            l-phenol      after 5 weeks                                                                          within 1 week                                     6      4-nitrosocarvacrol                                                                           Rust occurred                                                                          Rust occurred                                                          after 5 weeks                                                                          within 1 week                                     7      6-nitroso-o-cresol                                                                           Rust occurred                                                                          Rust occurred                                                          after 5 weeks                                                                          within 1 week                                     8      4-nitroso-m-cresol                                                                           Rust occurred                                                                          Rust occurred                                                          after 5 weeks                                                                          within 1 week                                     9      o-nitroso-phenol                                                                             No rust in 5                                                                           Rust occurred                                                          weeks   within 1 week                                     10     2-nitrosoresorcin                                                                            No rust in 5                                                                           Rust occurred                                                          weeks   within 1 week                                     11     4-nitrosoresorcin                                                                            No rust in 5                                                                           Rust occurred                                                          weeks   within 1 week                                     12     2-nitrosoresorcin                                                                            No rust in 5                                                                           Rust occurred                                            monomethylether                                                                              weeks   within 1 week                                     13     N--nitrosophenyl-                                                                            Rust occurred                                                                          Rust occurred                                            hydroxylamine ammonium                                                                       after 5 weeks                                                                          within 1 week                                     14     p-nitrosophenol                                                                              Rust occurred                                                                          Rust occurred                                                          after 5 weeks                                                                          within 1 week                                     15     2-nitroso-1-naphthol-                                                                        Rust occurred                                                                          Rust occurred                                            4-sulfonic acid                                                                              after 5 weeks                                                                          within 1 week                                     16     5-nitroso-8-quinolinol                                                                       Rust occurred                                                                          Rust occurred                                                          after 5 weeks                                                                          within 1 week                                     Comparative                                                                           (Excluding any anti-                                                                         Rust occurred                                                                          Rust occurred                                     Exam-  corrosive agent)                                                                             after 2 weeks                                                                          within 1 week                                     ple                                                                            __________________________________________________________________________

EXAMPLE 2

A 10 μm thick polyester film having wave form rough projections with a surface roughness R_(max) =about 300 .solthalfcircle. was run along a cylindrical can in a vacuum of 5×10⁻⁵ Torr into which oxygen was introduced at the rate of 0.3 l/min and subjected to continuous oblique deposition. The oblique deposition was conducted by depositing a CoNi alloy having an Ni content of 20% by weight and fused by means of electron beam heating with the alloy of an incident angle of 30° or less being cut off, so as to form an oxygen-containing CoNi thin ferromagnetic layer having a thickness of 1,000 Å. This will be termed Sample A.

Another sample was prepared under similar conditions except that the vacuum was at 5×10⁻⁶ Torr and the deposition was conducted without the introduction of oxygen, to form a CoNi thin ferromagnetic layer containing no oxygen. This sample will be referred to as Sample B.

From measurement of the amount of oxygen in the coating by means of the Auger electron spectrometry analysis, it was found that the average amount of oxygen in the coating of Sample A was 10% as an amount ratio of oxygen to the sum of Co and Ni (Oxygen/(CO+Ni)×100) whereas the amount of oxygen in the coating of Sample B was less than 1%.

Coated onto the surface of these samples were solutions of various anti-corrosive agents in water, alcohol, acetone, ethyl acetate, toluene or the like, and the adsorbed layer of the anti-corrosive agent was formed on the sample surface by washing the sample with the solvent used and drying. A lubricant layer was formed on the adsorbed anti-corrosive agent layer by coating and drying a dilution of each of various lubricants in a solvent. In instances where no appropriate solvent was found, the sample was heated in a vacuum, atmosphere or inert gases to expose the sample surface to a lubricant vapor and form the lubricant layer. In each case, the thickness of the lubricant layer was prepared to be within the range of 10 to 100 mg/m².

The sample was then slit into a desired width to produce a magnetic tape which was in turn placed in an atmosphere of 50° C. and 90% relative humidity. Sample A was measured every 3 days to determine the degree of clogging of a magnetic head by conducting recording and reproduction with a video deck. At the same time, microscopic observations of the surface of the magnetic layer were carried out to determine the degree of rust occurrence. Sample B was tested daily in substantially the same manner. The results are shown in Table 7 which follows.

                                      TABLE 7                                      __________________________________________________________________________     No.;Compar-                                                                    ative Exam-                                                                    ples in pa-                                                                           Class of                                                                            Anti-corrosive Day of rust                                                                           Day of occurrence                            rentheses                                                                             samples                                                                             agents   Lubricant                                                                            occurrence                                                                            of clogging                                  __________________________________________________________________________     1      B    dinonyl naphtha-                                                                        stearic acid                                                                         4th day                                                                               3rd day                                                  lene sulfonate                                                                          amide                                                     (2)    B    --       --    1st day                                                                               1st day                                      (3)    B    --       stearic acid                                                                         2nd day                                                                               1st day                                                           amide                                                     4      B    dicyclohexyl                                                                            stearic acid                                                                         5th day                                                                               4th day                                                  ammonium nitrite                                                                        amide                                                     (5)    B    dicyclohexyl                                                                            --    6th day                                                                               1st day                                                  ammonium nitrite                                                   6      A    2-tert.-butyl-                                                                          Ni stearate                                                                          Not occurred                                                                          15th day                                                 catechol       in 30 days                                          (7)    A    --       Ni stearate                                                                          15th day                                                                              6th day                                      (8)    A    2-tert.-butyl-                                                                          --    Not occurred                                                                          3rd day                                                  catechol       in 30 days                                          9      A    4,4'-diamino-                                                                           stearic acid                                                                         21th day                                                                              15th day                                                 benzophenone                                                                            amide                                                     (10)   A    --       --    12th day                                                                              6th day                                      11     A    1,2-naphtha-                                                                            n-tridecane                                                                          Not occurred                                                                          15th day                                                 lene diol      in 30 days                                          (12)   A    --       n-tridecane                                                                          Not occurred                                                                          9th day                                                                 in 15 days                                          13     A    2-amino-l-                                                                              cetylalcohol                                                                         30th day                                                                              21th day                                                 naphthol                                                           14     A    2-amino-l-                                                                              n-tridecane                                                                          30th day                                                                              30th day                                                 naphthol                                                           15     A    2-amino-l-                                                                              cleic acid                                                                           30th day                                                                              24th day                                                 naphthol                                                           16     A    2-amino-l-                                                                              Ni perfluc-                                                                          30th day                                                                              24th day                                                 naphthol roalkyl sul-                                                                   fonate                                                    17     A    2-amino-l-                                                                              Ni perfluc-                                                                          Not occurred                                                                          30th day                                                 naphthol/2-ni-                                                                          roalkyl sul-                                                                         in 30 days                                                      troso-resorcin                                                                          fonate                                                                (1:1)                                                              18     A    2-amino-l-                                                                              polydimeth-                                                                          Not occurred                                                                          27th day                                                 naphthol/2-ni-                                                                          ylsiloxane/                                                                          in 30 days                                                      troso-resorcin                                                                          stearic acid                                                          (1:1)    amide (1:1)                                               19     A    α-benzoin-                                                                        polydimeth-                                                                          30th day                                                                              21th day                                                 oxime    ylsiloxane                                                20     A    1,2-naphtho-                                                                            polydimeth-                                                                          30th day                                                                              27th day                                                 quinone  ylsiloxane                                                __________________________________________________________________________

EXAMPLE 3

Using Sample A and Sample B obtained in Example 2, a solution of each of various anti-corrosive agents in a solvent such as ethyl alcohol, acetone, ethyl acetate, toluene or the like was coated onto the surface of the sample and the coating was dried to form an adsorbed layer of the anti-corrosive agent. The amount of the coating was adjusted to be about 10 mg/m². Coated on the back surface of the polyester film was a solution of a lubricant in said solvent, and the coating was dried to form the lubricant layer. The amount of coating of the lubricant was in the range of 10 to 100 mg/m². After the sample was wound in a roll and maintained at 30° C. for 10 hours, it was slit into a desired width to give a magnetic tape sample. This tape sample was then placed in an atmosphere of 50° C. and 90% relative humidity. Sample A was measured every 3 days to determine the occurrence of clogging by subjecting the tape sample to recording and reproduction with a video deck. Sample B was measured likewise daily. At the same time, both samples were measured microscopically to determine the degree of rust occurrence. The results are shown in Table 8 which follows.

                                      TABLE 8                                      __________________________________________________________________________     No.;Compar-                                                                    ative Exam-                                                                    ples in pa-                                                                           Class of                                                                            Anti-corrosive  Day of rust                                                                           Day of occurrence                           rentheses                                                                             samples                                                                             agents   Lubricant                                                                             occurrence                                                                            of clogging                                 __________________________________________________________________________     1      B    dinonyl naph-                                                                           stearic acid                                                                          5th day                                                                               3rd day                                                 thalenesul-                                                                             amide                                                                 fonate                                                             2      B    dinonyl naph-                                                                           polydimethyl                                                                          5th day                                                                               2nd day                                                 thalenesul-                                                                             siloxane                                                              fonate                                                             (3)    B    --       polydimethyl                                                                          1st day                                                                               1st day                                                          siloxane                                                  4      B    dicyclohexyl                                                                            stearic acid                                                                          6th day                                                                               3rd day                                                 ammonium nitrite                                                                        amide                                                     (5)    B    dicyclohexyl                                                                            stearic acid                                                                          6th day                                                                               1st day                                                 ammonium nitrite                                                                        amide                                                     6      A    2-tert.-butyl-                                                                          nickel stea-                                                                          Not occurred                                                                          15th day                                                catechol rate   in 30 days                                         (7)    A    --       nickel stea-                                                                          15th day                                                                              5th day                                                          rate                                                      (8)    A    2-tert.-butyl-                                                                          --     Not occurred                                                                          3rd day                                                 catechol        in 30 days                                         9      A    4,4'-diamino-                                                                           stearic acid                                                                          30th day                                                                              12th day                                                benzophenone                                                                            amide                                                     10     A    1,2-naphthalene                                                                         n-tridecane                                                                           Not occurred                                                                          15th day                                                diol            in 30 days                                         11     A    2-amino-1-                                                                              cetylalcohol                                                                          30th day                                                                              15th day                                                naphthol                                                           12     A    2-amino-1-                                                                              n-tridecane                                                                           Not occurred                                                                          30th day                                                naphthol        in 30 days                                         13     A    2-amino-1-                                                                              oleic acid                                                                            Not occurred                                                                          30th day                                                naphthol        in 30 days                                         14     A    2-amino-1-                                                                              Ni perflu-                                                                            Not occurred                                                                          30th day                                                naphthol oroalkyl                                                                              in 30 days                                                              sulfonate                                                 15     A    2-amino-1-                                                                              Ni perflu-                                                                            Not occurred                                                                          Not occurred                                            naphthol/2-ni-                                                                          oroalkyl                                                                              in 30 days                                                                            in 30 days                                              trosoresorcin                                                                           sulfonate                                                             (1:1)                                                              16     A    2-amino-1-                                                                              polydimeth-                                                                           Not occurred                                                                          Not occurred                                            naphthol/2-ni-                                                                          ylsiloxane                                                                            in 30 days                                                                            in 30 days                                              trosoresorcin                                                                           stearic acid                                                          (1:1)    amide (1:1)                                               17     A    α-benzoinoxime                                                                    polydimeth-                                                                           30th day                                                                              15th day                                                         yl siloxane                                               18     A    1,2-naptho-                                                                             polydimeth-                                                                           Not occurred                                                                          30th day                                                quinone  yl siloxane                                                                           in 30 days                                         __________________________________________________________________________

Although each of the above examples relates to the CoNi-series magnetic layer, Co thin layers, Fe-Ni thin layers, Fe-Co thin layers and so on produced similar results. It is to be noted that thin ferromagnetic layers containing oxygen receive greater effects than thin layers containing no oxygen, this tendency being significant for an oxygen content ranging from 3 to 45%.

EFFECT OF THE INVENTION

As has been apparent from the previous description of the specification, the magnetic recording medium according to the present invention has overall durability, including corrosion resistance and travel performance, and no clogging tendency, so that it has great practical advantage. 

What is claimed is:
 1. A magnetic recording medium having an oxygen-containing thin ferromagnetic metal layer formed on a nonmagnetic substrate, wherein at least one compound, capable of suppressing hydration of ferromagnetic metal ions by acting upon the ionized ferromagnetic metal, selected from the group consisting of dihydric phenols, diaryl ketones, alkyl phenols, naphthols, quinones, nitroso compounds and oxime compounds is introduced on or around said thin ferromagnetic metal layer.
 2. A magnetic recording medium according to claim 1 wherein said compound is a member selected from the group consisting of hydroquinone, resorcin, catechol, 2-methylhydroquinone, 4-methylresorcinol, 5methylresorcinol, 4-methylpyrocatechol, 2,5-dimethylhydroquinone, 4,6-dimethylresorcinol, 2,5-dimethylresorcinol, 2-isopropyl-5-methylhydroquinone, 2-tert.-butylhydroquinone, 2,5-di-tert.-butylhydroquinone, 4-tert.-butylcatechol, 2-aminoresorcinol, 2-nitroresorcinol, 2,5-dichlorohydroquinone, benzophenone, 4-methylbenzophenone, 3-methylbenzophenone, 3,4-dimethylbenzophenone, 4,4'-dimethylbenzophenone, 3,4'-dimethylbenzophenone, 4-ethylbenzophenone, 4-hydroxybenzophenone, 4,4'-dihydroxybenzophenone, 2,3,4-trihydroxybenzophenone, 2,4-dihydroxybenzophenone, 2,2',5,6'-tetrahydroxybenzophenone, 2,3',4,4',6-pentahydroxybenzophenone, 4-aminobenzophenone, 4,4'-diaminobenzophenone, 4-methoxy-2-hydroxybenzophenone, 2,2'-dihydroxy-4,4'-dimethoxybenzophenone, 2,6-dihydroxy-4-methoxybenzophenone, o-cresol, m-cresol, p-cresol, o-ethylphenol, m-ethylphenol, p-ethylphenol, 2,3-dimethylphenol, 2,5-dimethylphenol, 2,6-dimethylphenol, 3,4-dimethylphenol, 3,5-dimethylphenol, 2,4,6-trimethylphenol, 2,4,5-trimethylphenol, 5-isopropyl-2-methylphenol, 2-isopropyl-5-methylphenol, p-tert.-butylphenol, 2,6-di-tert.-butyl-p-cresol, 4,4'-methylenebis-2,6-di-tert.-butylphenol, 2,6-dimethyl-4-tert.-butylphenol, 2-tert.-amyl-4-methylphenol, 2-methyl-4,6-di-tert.-butylphenol, 2,4,6-tri-tert.-butylphenol, α-naphthol, β-naphthol, 1,2-naphthalenediol, 1,4,5-naphthalenetriol, 1,2,5,8-naphthalenetetraol, 1-chloro-2-naphthol, 2,4-dichloro-1-naphthol, 1-nitro-2-naphthol, 1,6-dinitro-2-naphthol, 1-nitroso-2-naphthol, 2-nitroso-1-naphthol, 1-amino-2-naphthol, p-benzoquinone, o-benzoquinone, 1,2-naphthoquinone, 1,4-naphthoquinone, 2,6-naphthoquinone, anthraquinone, 9,10-phenanthrenequinone, diphenoquinone, methyl-p-benzoquinone, 2,3-dimethyl-p-benzoquinone, 2-methyl-1,4-naphthoquinone, 2-methylanthraquinone, 2,5-dihydroxy-p-benzoquinone, tetrahydroxy-p-benzoquinone, 5-hydroxy-1,4-naphthoquinone, 2,3-dihydroxy-1,4-naphthoquinone, 5,8-dihydroxy-1,4-naphthoquinone, 2-hydroxyanthraquinone, 1,2-dihydroxyanthraquinone, 1,2,3-trihydroxyanthraquinone, 1,2,4-trihydroxyanthraquinone, 1,2,5-trihydroxyanthraquinone, 1,2,6-trihydroxyanthraquinone, 1,2,7-trihydroxyanthraquinone, 2-aminoanthraquinone, 1,2-diaminoanthraquinone, 1-nitroanthraquinone, 1,5-dinitroanthraquinone, 2,6-dichloro-p-benzoquinone, tetrachloro-p-benzoquinone, tetrafluoro-p-benzoquinone, 2,5-dichloro-3,6-dihydroxy-p-benzoquinone, 1-methyl-2-hydroxy-1,4-naphthoquinone, 1-nitroso-2-naphthol, 2-nitroso-1-naphthol, 1-nitroso-2-naphthol-3,6-disulphonic acid sodium salt, 4-nitroso-2-methoxy-1-phenol, 4-nitroso-2-ethoxy-1-phenol, 4-nitrosocarvacrol, 6-nitroso-o-cresol, 4-nitroso-m-cresol, o-nitrosophenol, 2-nitrosocresorcin, 4-nitrosoresorcin, 2-nitrosoresorcin monomethylether, N-nitrosophenyl hydroxylamine ammonium salt, p-nitrosophenol, 2-nitroso-1-naphthol-4-sulphonic acid, 5-nitroso-8-quinolinol, benzyloxime, glyoxime, benzaldoxime, benzamidoxime, α-benzoinoxime, acetophenone oxime, benzophenone oxime, dimethylglyoxime, salicylaldoxime, 2,4-dimethyl phenol, tetrabromo-p-benzoquinone and 1-methyl-2-hydroxy-p-benzoquinone.
 3. A magnetic recording medium according to claim 1, characterized in that a thin layer of said compound is formed on a surface of said thin ferromagnetic metal layer.
 4. A magnetic recording medium according to claim 1, characterized in that said compound is present at least on a surface of said nonmagnetic substrate on which said thin ferromagnetic metal layer is formed.
 5. A magnetic recording medium according to claim 1 wherein said compound is present in an amount between about 0.5 and 500 mg per square meter of said medium.
 6. A magnetic recording medium having an oxygen-containing thin ferromagnetic metal layer formed on a nonmagnetic substrate wherein at least one compound capable of suppressing hydration of ferromagnetic metal ions upon ionization of a ferromagnetic metal selected from the group consisting of dihydric phenols, diaryl ketones, alkyl phenols, naphthols, quinones, nitroso compounds and oxime compounds is introduced on or around said thin ferromagnetic metal layer, and a lubricant is applied onto said thin ferromagnetic metal layer.
 7. A magnetic recording medium according to claim 6 wherein said lubricant is present in an amount between 0.5 and 500 mg per square meter of said medium.
 8. A magnetic recording medium according to claim 7 wherein said amount is between 5 and 200 mg per square meter of said medium.
 9. A magnetic recording medium having an oxygen-containing thin ferromagnetic metal layer formed on a nonmagnetic substrate wherein said thin ferromagnetic metal layer having introduced on or around it a compound capable of suppressing hydration of ferromagnetic metal ions, by acting upon the ionized ferromagnetic metal, selected from the group consisting of dihydric phenols, diaryl ketones, alkyl phenols, naphthols, quinones, nitroso compounds and oxime compounds is formed on one surface of said non-magnetic substrate which is flexible and elongated and a lubricant-containing layer is formed on the other surface thereof.
 10. A magnetic recording medium according to claim 9 wherein said lubricant is present in an amount between 0.5 and 500 mg per square meter of said medium. 